Photographic diazotype composition and heat development thereof



Patented Sept. 22, 1953 PHOTOGRAPHIC DIAZOTYPE COMPOSITION AND HEAT DEVELOPMENT THEREOF Harold G, Glieig, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Application January 31, 1950, Serial No. 141,581

12 Claims. (Cl.- 9. -6)

diazonium compound, which may, for example, be

pi-diethylamino benzene diazonium chloride, reacts with an azo dye coupl r, such as phloroglucinol, with which the stratum can be treated later, or which can be incorporated into the original stratum to form an intensely colored, darkhued azo dye. However, upon previous exposure to light, particularly strongly actinic light, such as that having a wave length range of 3400 A. to 4100 A, the diazonium compound decomposes in a relatively few seconds, and, after alkalizing, will no longer react to form the dye.

The image reproduction is generally effected y exposing the stabiliz d sensi ive s ra um 0 actinic light reflected from or transmitted through the image to be copied. The exposed portion are thereby deactivated in proportion to the intensity of the exposure. When the exposure is completed, the image reproduction is developed .by rendering the stratum alkaline, usually by treating it with moist ammonia gas where the maximum convenience and simplicity desired. The dye formation is accordingly distributed to form a replica of the image.

A disadvantage of the diazotype process, as previously practiced, has been the'type of chemical treatment required for the developing step. In the gaseous developing treatment, as described above, the stratum containing the light-sensitive material can be kept dry to the touch throughout the image-reproducing process, thereby avoiding the awkwardness of a cumbersome drying operation. Because of this convenience, gaseous development has been widely used.

However, the gaseous development process does have certain disadvantages and unsatisfactory features. The process requires use of a gas-.- producing source as well as a development chamber to confine the ammonia gas which is highly irritating to the lungs and eyes.

The process of the present invention does not have the disadvantages of the gaseous developing process or the solution type developing process.

In general, the process of the present invention comprises diazoty-pe paper impregnated or coated with a providing a light-sensitive composition in which a mixture of a light-sensitive diazonium compound and an azo dye coupler is stabilized with an acid which is readily decomposed by heat, exposing the paper to actinic light distributed to correspond to the image to be reproduced, and developing the latent image by heating to decompose the heat-decomposable acid.

One object of the present invention is to pro- Vide an improved process of developing lightsensitive diazonium compounds.

Another object of the invention is to provide an improved process of reproducing images formed from colored diazonium salts.

Another object of the invention is to provide an improvement in the .diazotype process wherein neither solutions nor gases are required to develop the latent image.

Another object of the invention is to provide an improvement inthe .diazotype process wherein the image is developed by heat alone, with- Dllt any treatment with an alkaline developer.

Another object of the invention is to provide a simplification of the diazotype process.

Another object of the invention is to provide an improved diazotype sensitizing solution. St l another object oi th invention is to pro- .vide a support sheet carrying an improved lightsensitive composition to be used in a diazotype process.

These and other objects will be more apparent and the invention will be more readily understood from the following description.

One method of carrying out the present invention is first to treat a sheet of carrier sup--. port material with a solution of a diazonium salt and an .azo dye coupler and then to treat the sheet with a composition including a heatcnsitive acid and a salt of the acid, for stabilizing the mixture of the diazonium compound and the coupler. The heat-sensitive acid is preferably trichloroacetic acid since this compound, although stable at all ordinary temperatures of use, may be readily decomposed using moderately elevated temperatures of C. and above. It is also possible, with less satisfactory results, to use solutions of other strongly ionizable acids readily decomposed by heating to moderately high temperatures. Trichloroacetic acid is preierred from another standpoint besides the fact that it may be readily decomposed by heating. This acid has a very high dissociation constant. At 25 C. the dissociation constant (-ka.) is 1.2 and the percent ionized at this temperature, in a 0.3 molar solution, is 89.5.

Tre

of the carrier sheet is preferably carried out by spreading a uniform film of solution over a sur face of the sheet. In this way, a surface stratum of sensitized material is formed. It is also possible, however, to impregnate the carrier thoroughly with the sensitized material by soaking the carrier support sheet in the sensitizing solutions. The sheet may be paper, cloth, transparent cellulosic material such as cellophane, or'

cellulose nitrate, and the like. After the treatment, the sheet is dried and is then ready for use. A more specific example of this method follows:

Example I A sheet of paper is coated with a solution comprising 50 parts by weight of water, 1 part by weight of the fiuoboric acid salt of p-diazodiethylaniline, and 0.2 part by weight of phloroglucinol, the latter serving as the azo dye coupler. The paper is then dried and, at any later time, is treated with a solution comprising 50 parts by weight of acetone, 5.5 parts by weight of trichloracetic acid, and 3.0 parts by weight of diethanolamine. The acetone is used merely as a solvent which evaporates readily without leaching out the coating of diazonium salt already on the paper. The diethanolamine is used for the purpose of neutralizing part of the acid to get a desirable concentration of a salt of the trichloracetic acid. Other volatile organic solvents may be used in place of the acetone but the solvent must be one which does not dissolve the diazonium compound. Other bases, such as sodium, potassium, or ammonium hydroxides, and monoor tri-ethanolamine may be used in place of the di-ethanolamine.

The paper, treated as thus described, may be dried and then printed in the usual manner by, first, exposing it to an image to be reproduced, in a. mercury arc printer, and then ironing or otherwise applying suflicient heat to decompose the heat-sensitive acid. The intensity of heat used should be just below that which would scorch the paper. The temperature may be from about 100 to just below the scorching temperature of the paper used. I

Decomposition of the acid probably raises the pH of the material with which the paper has been treated. Raising of the pH permits the phloroglucinol to react with the diazonium compound in all areas not previously affected by the light in the printer to a sufiicient extent to cause complete dissociation of the diazonium salt. Reaction between the coupler and the diazonium compound causes formation of a colored image corresponding to that presented to the sensitized paper within the printer.

Instead of the type of process described in Example I, there may be used a process in which the diazonium salt, the coupler, and the heatsensitive stabilizing acid are in the same treating solution.

' Example II A blank sheet of paper may be coated or impregnated with a solution of:

50 parts water 2.5 parts trichloracetic acid 0.6 part sodium hydroxide 1.0 part p-diazodiethylaniline (fiuoboric acid salt) 0.2 part phloroglucinol (all parts being by weight) This solution has a pH of about 2.5. After treating the paper with the above solution, the sheet is dried and the remainder of the process carried out as described in Example I.

Example III The carrier sheet may be treated with a solution consisting essentially of:

This solution has a pH of about 2.3. The remainder of the process is as described in the previous examples.

Example IV The carrier sheet may be treated with a solution consisting essentially of:

50 parts water 3 parts trichloracetic acid 1.1 parts potassium hydroxide 1.0 part p-diazodiethylaniline salt) 0.2 part phloroglucinol (all parts being by weight) This solution has a. pH of 2.1 approximately. The remainder of the process is the same as that described in previous examples.

Example V This example is the same as Example IV with the exception that 1.26 parts by weight of ammonium hydroxide (28%) are used in place of potassium hydroxide. This solution has a pH of about 2.3.

(zinc chloride Example VI This example is the same as Example IV with the exception that 1.3 parts by weight of 2-diazo- S-diethylamino toluene are used in place of pdiazodiethyl aniline.

Example VII Same as Example IV except that 1.0 part of p-diazo-diphenylamine is used in place of pdiazodiethyl aniline.

Example VIII Same as Example V with 2.0 parts by weight of tartaric acid added for the purpose of increasing stability during long periods of storage.

The function of the alkali in the above compositions is to react with part of the trichloroacetic acid in order to form a salt of the acid. The proportion of salt to acid should always be minor but, for best results, some salt appears to be necessary. The function of the salt is not understood entirely and the process is operative without any appreciable quantities being present. However, in the preferred form of the method, the salt should be present.

The sensitizing composition including the heatsensitive acid should always have a low value of pH. It is preferred that the pH be less than 3.

Any of the couplers commonly used in diazotype work can be used in the process of the present invention. An example of a coupler, other than phloroglucinol, which works well in the process, is resorcinol.

What is claimed is:

1. In a process for reproducing images, the steps of: providing a stratum containing a lightsensitive diazonium compound stabilized with trichloracetic acid, exposing the stratum to actinic light distributed to correspond to the image to be reproduced for deactivating the illuminated stratum portions; and developing the image reproduction by heating the exposed stratum in the presence of a salt of said acid selected from the class consisting of sodium, po tassium, ammonium, and mono-, di-, and triethanolamine salts and in the presence of an azo dye coupler to decompose the stabilizing trichloracetic acid and cause the production of the diazotype color.

2. A method according to claim 1 in which said stratum contains the azo coupler, and when wet has a, pH of about 3 or less.

3. A method according to claim 2 in which the diazonium compound is a salt of p-diazodiethylaniline, and the coupler is phloroglucinol.

i. In a process for preparing diazotype reproductions of images Without the application of external developing chemicals, the steps of preparing a stratum containing a ligh -sensitive diazonium compound, an azo dye coupler and trichloracetic acid, exposing the stratum to actinic light distributed to correspond to the image to be reproduced for at least partially deactivating the illuminated stratum portions; and developing the image reproduction by heating the exposed stratum in the presence of a salt of said acid selected from the class consisting of sodium, potassium, ammonium, and mono-, di-, and triethanolamine salts to decompose the trichloracetic acid and cause the stratum to increase in alkalinity and become colored in inverse relation to the extent of deactivation.

5. In an acid-stabilized diazotype copying composition, a light-sensitive, acid-stabilizable diazonium compound, an azo dye coupler and heat-sensitive stabilizing material including trichloracetic acid and a salt selected from the class consisting of sodium, potassium, ammonium, and mono-, di-, and triethanolamine salts of said acid, for decomposition upon heating to increase the alkalinity of the composition and bring about dye formation.

6. In a diazotype image-copying process, the steps of: providing a diazotype copying stratum containing an acid-stabilized, light-sensitive diazonium compound and an azo dye coupler; moistening the stratum with a solution of trichloracetic acid containing a minor proportion of a salt selected from the class consisting of sodium, potassium, ammonium, and mono-, di-,

and triethanolamine salts of said acid, in a liquid which dissolves neither the diazonium compound nor the coupler; drying the moistened stratum; exposing the stratum to actinic light distributed to correspond to an image to be copied; and heating the exposed and dried stratum to decompose the trichloracetic acid for increasing the alkalinity and causing development of the image reproduction in diazotype color.

7. A method according to claim 6 in which the liquid is essentially non-aqueous.

8. In a process for rendering heat-developable a diazotype image-copying stratum containing an acid-stabilized, light-sensitive diazonium compound and an azo dye coupler; the step of moistening the stratum with a solution of trichloracetic acid containing a minor proportion of a salt selected from the class consisting of sodium, potassium, ammonium, and mono-, di-, and triethanolamine salts of said acid, in a liquid that dissolves neither the diazonium compound nor the coupler.

9. A method according to claim 8 characterized by the further step of drying the moistened stratum to evaporate off the liquid.

10. A member for reproducing an image comprising a carrier support in the form of a sheet, said sheet carrying a, stratum including a composition comprising a light-sensitive stabilized diazonium compound, an azo coupler, trichloroacetic acid, and a salt of said acid selected from the class consisting of sodium, potassium, ammonium, and mono-, di-, and triethanolamine salts.

11. A member according to claim 10 in which said diazonium compound is a salt of p-diazodiethyl-aniline and said coupler is phlorogluci- 1101.

12. A member according to claim 10 in which said coupler is resorcinol.

HAROLD G. GREIG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 20,708 Hinman Apr. 26, 1938 2,217,189 Sus Oct. 8, 1940 2,429,249 Von Glahn Oct. 21, 1947 FOREIGN PATENTS Number Country Date 427,962 Great Britain Apr. 29, 1935- 570,027 Great Britain June 19, 195 

1. IN A PROCESS FOR REPRODUCING IMAGES, THE STEPS OF: PROVIDING A STRATUM CONTAINING A LIGHTSENSITIVE DIAZONIUM COMPOUND STABILIZED WITH TRICHLORACETIC ACID, EXPOSING THE STRATUM TO ACTINIC LIGHT DISTRIBUTED TO CORRESPOND TO THE IMAGE TO BE REPRODUCED FOR DEACTIVATING THE ILLUMINATED STRATUM PORTIONS: AND DEVELOPING THE IMAGE REPRODUCTION BY HEATING THE EXPOSED STRATUM IN THE PRESENCE OF A SALT OF SAID ACID SELECTED FROM THE CLASS CONSISTING OF SODIUM, POTASSIUM, AMMONIUM, AND MONO-, DI-, AND TRIETHANOLAMINE SALTS AND IN THE PRESENCE OF AN AZO DYE COUPLER TO DECOMPOSE THE STABILIZING TRICHLORACETIC ACID AND CAUSE THE PRODUCTION OF THE DIAZOTYPE COLOR. 